Film digitization using flatbed scanners can be a practical alternative to direct digital image capture or other means of digital image acquisition such as storage phosphor computed radiography. For example, hybrid imaging systems can provide an expedient and low cost imaging solution for both dentists and insurance companies. Without the more significant capital investment required for other digital devices, the dental practitioner can have the advantages that the digital modality can offer, such as imaging capability to support practice management and electronic insurance claims. Insurance companies are also motivated to incorporate imaging into electronic claims in order to reduce overhead associated with manual claims submission.
An important step in any hybrid imaging system is the initial image capture, which for film digitization is the scanning process. Exposure conditions should be carefully controlled during image acquisition so that any subsequent processing steps can be implemented in a more desired fashion. In practice this means controlling unwanted exposure or flare and maintaining proper alignment of the scanned image with the optical configuration of the scanner. Because the relative size of the platen on a flatbed scanner is great compared to a small format film such as a smaller format dental radiograph, the concern over unwanted flare becomes an issue.
Dental radiographs vary greatly in practice. X-ray exposure levels and processing of these films contribute to variability of dental films. A dental film can range from a very light "under-exposed" image to a very dark in appearance "over-exposed" image. Where there is too much exposure on the platen when scanning an under-exposed radiograph, for example, the captured image will not have enough gray value content. Another important consideration during image capture is the alignment of the radiograph on the platen in the correct horizontal and vertical directions to maintain consistency with, for example, the CCD array of a scanner. If the image does not correspond to this alignment when placed on the platen, image rotation may be required, which can alter the aspect ratio of the original image.
One other consideration in the placement of dental radiographs on the platen relates to the actual viewing of the image so that the anatomical structures will be seen digitally in the same orientation as seen on the original radiograph. Smaller format dental films contain a dimple that, when observed properly, points outward toward the viewer in a position corresponding to standard practices in dentistry. Placing the film on the platen in a manner corresponding to this practice can avoid flipping the digital image so that the perspective remains the same as in the radiograph.
U.S. Pat. No. 5,483,325 describes an accessory frame that can be mounted on a photocopier or electronic flatbed scanner that facilitates location and removal of small originals like business cards. This patent does not address the problems described above relating to digitization of small format films using a flatbed scanner, such as regulating exposure and aligning the films on the platen consistent in a manner that is useful to the dental practitioner. This patent does not address the problem of flare in copying transparent originals.